Ultrasonic booster can change the amplitude of transducer. Booster is a passive device and cannot produce vibration itself. It is only to output after the input vibration is changed into amplitude, and finishing the impedance conversion at the same time. Under the stimulus of electric field, ultrasonic transducer can produce regular vibration and the amplitude is about 10μmm commonly. That is not enough to finish the welding and processing step directly. Through with the suitable booster, the amplitude of ultrasonic can be changed in a large range. If the material is enough intensive, the amplitude can exceed 100μmm. We named oscillator after connecting ultrasonic transducer with booster. On the other hand, when the booster works vibration through longitudinal and extension, on the both sides of the particle direction of motion is the opposite, which is equal to a rest section. This section is named nodal point, which is the best-fixed point of the oscillator. To departure from the fixed point, it will reduce the work efficiency of the oscillator. In the general, the transform efficiency of aluminum booster is high but the intension of material is low and easy to cracking and easy to slipping from the hole of screw; the intension of the steel booster is high but the sound impedance is large comparatively; the all round properties of the titanium alloy booster is good but the price is high and the processing is difficult.